1. Field of the Invention
This invention relates to gas turbines. More specifically, the invention relates to a fan frame for a gas turbine.
2. Description of the Related Art
Gas turbine engines include an engine core and a fan section. In aircraft, the engine core is disposed on the airframe and has a primary flowpath. The fan section is disposed coaxial with and radially outward of the engine core, and has a secondary flowpath. A fan cowling envelops the fan section and outwardly bounds the secondary flowpath. An area of concern with gas turbine engines is the structural mounting of the fan section with the engine core. The mounting structure is required to transfer all the operational loads, such as structural, thrust and aerodynamic loads, to the fan frame and thence to the airframe.
With reference to FIG. 1, a mounting structure for a turbofan including an engine core and a fan assembly is described in U.S. Pat. No. 5,471,743. The fan assembly has a fan disk and a plurality of fan blades, which extend outwardly across the flowpath. A fan cowling extends circumferentially about the blades and a plurality of fan exit case guide vanes. The fan exit case guide vanes are attached to the fan cowling and to a support cone, which are disposed between the engine core and the plurality of guide vanes. An intermediate case structurally connects the fan cowling to the engine core. The intermediate case includes a plurality of struts and an outer ring or fan exit case rear. The struts extend from the inner platform of the engine core to the outer ring. Each of the struts is hollow to reduce weight and circumferentially continuous about a spanwise axis of the strut. The outer ring connects the intermediate case with the fan cowling through a bolted connection. Each of the struts has a joint radially located near the inner flow surface of the fan assembly.
In the above-described mounting configuration, separate guide vanes and struts are utilized. However, shorter distances between the back of fan blades and the fan exit guide vanes generally increase noise produced by the fan assembly. Thus, there is a need for a fan frame or assembly that reduces noise while maintaining structural integrity.